ok here is a quick reference. doepfer and analog solutions are euro rack size and use mini jack cables(1/8") they are pretty decent but "budget" modulars
blacet and wiard make an affordable approach that uses mini jacks and they fit into affordable frack racks. these are definitely a step up from the doepfers and use high quality parts.
then the "pro sumer" stuff would be Modcan it uses standard 1/4" jacks but each module is around 300-500 plus the power supply is 300 alone.
the more expensive stuff i cant comment on because i have no hands on with it. i like and use all the stuff above, but if pressed i would reccomend going the
www.blacet.com and
www.wiard.com way i like their build quality and the service is great, also with the blacets if you have any soldering skills you can save money by purchasing kits.
imo the best way to build a mod synth is to buy filters and delays and distortions first, so you can go ahead and use it as a filterbank for your exhisting gear, then when you have built up a sweet filterbank start buying VCOs, ADSRs, and midi to cv modules or a cv sequencer howecer you want to go. READ READ READ as much as you can before making any purchases, modular synthesis takes a while to really get a grip on, so unless you have a lot of practice on softsynths or somthing else you need to research like hell for a while.
